sysroot: Add ostree_sysroot_write_deployments_with_options()

sysroot: Add ostree_sysroot_write_deployments_with_options()

More sophisticated users of libostree like rpm-ostree need control over things
like the system repository. Previously we introduced a "no cleanup" flag to
`ostree_sysroot_simple_write_deployment()`, but that's a high level API that
does filtering on its own.

Since rpm-ostree needs more control, let's expose the bare essentials of the
"sysroot commit" operation with an extensible options structure, where one of
the options is whether or not to do post-transaction repository operations.

Closes: #745
Approved by: jlebon